Various small engines, such as model airplane engines, are started manually utilizing a glow plug. The glow plug heats the fuel-air mixture so that the fuel-air mixture can ignite to initiate engine operation.
The glow plug is a resistance element which is heated electrically by a glow plug driver. The resistance of the glow plug varies with temperature. During the engine starting operation, the temperature of the glow plug varies due to, for example, the cooling of the glow plug by the fuel. When the glow plug is cooled, its resistance drops, and it tends to draw more current. Ideally, the glow plug driver should provide more power to the glow plug as the glow plug cools.
Prior art glow plug drivers have not been particularly efficient in applying full battery voltage across the glow plug. Consequently, relatively large batteries have been required. Prior art glow plug drivers are also relatively large, and the output is sensitive to variations in values of many of the circuit components.